The present invention relates generally to banding rotors of electrodynamic machines and, more particularly, to improved rotor bands and a method for making and applying such bands.
The construction of rotors for electrodynamic machines is well known. For example, armatures for use in electric generators or motors comprise shafts on which laminations of magnetic materials are mounted and fixed together to form armature cores. Windings of the armatures are placed into slots formed in the armature cores and include end turns or loops which extend beyond the ends of the slots. On such rotors, measures must be taken to resist the centrifugal forces to which the windings are subjected in the open slots, and particularly, at their ends beyond the slots of the armature core where the windings are connected. Steel bands or wire have been used for this purpose to encircle various portions of the armature cores and the end portions of the windings.
While such metallic bands perform the winding retaining function, they also present several undesirable characteristics. For example, extreme care must be taken during installation of such bands to ensure that the bands do not cut into the winding insulation, particularly at the end portions of the windings where the bands lay directly over the windings. If such metallic bands cut into the winding insulation due to sharp edges, working loose or otherwise, the machine will fail.
An improvement in rotor banding was brought about by tightly wrapping under tension resin impregnated roves or webbing comprising fibers of glass, nylon, polyester or the like around an armature and curing the resulting wrappings to form a unitary band around the rotor. While such rotor banding provides an improvement over the metallic bands, this process presents its own undesirable characteristics which include the mess of handling the resin impregnated roves or webbing and the added time required for forming and curing the bands during the rotor manufacturing process. Additionally, since roves or webbing are used to form the bands, the individual fibers of the roves or webbing are oriented at varying angular orientations relative to the axis of the rotor. These varying orientations of the fibers reduce the strength of the resulting band which is maximized if all fibers are oriented as near to 90.degree. to the axis of the rotor as possible.
Accordingly, the need exists for an effective, maximum strength rotor band which can be quickly and conveniently installed during manufacture of the rotor without the mess and the additional time required to install the bands formed by winding and curing resin impregnated roves or webbing directly on the rotor.